1. Field of the Invention
The present invention relates to a flow control valve in which channels are switched by varying an applied current, and thus a flow rate is controlled.
2. Description of the Related Art
In the past, a linear motion-type electromagnetic proportional flow control valve, in which a spool slides axially in proportion to an applied current value, has been proposed as one type of electromagnetic flow control valve for controlling a flow rate of fluid according to an applied current value. Another flow control value is of the rotary motion type, wherein a valve is installed in a housing and a flow rate is controlled by rotating the valve with a motor.
The foregoing linear motion-type electromagnetic flow control value has an advantage that a flow rate can be controlled in proportion to an applied current. When mounted in an automobile, however, the flow control valve is likely to operate incorrectly because of the axial oscillation of the spool, and cannot control a flow rate with precision.
In contrast, the conventional rotary motion-type flow control value is unaffected by the above oscillation. However, since a large drive motor is needed, the control valve itself is large in size. The adoption of a structure, in which a reduction gear is employed to increase a rotary torque, enables the use of a small motor. However, the deceleration decreases response speed, disabling high-speed flow control.
When the above motor is used, a torque variation in a direction defined by a rotation angle, which is attributable to the non-uniform distribution of magnetic fields in the direction defined by a rotation angle of the motor, leads to poor linearity of the rotation angle relative to an applied current and eventually to the poor proportionality of a flow rate of controlled liquid relative to the applied current.